This invention relates to sprockets used with an endless belt of the type having internal drive lugs and, more particularly, to a self-cleaning sprocket for use with a crop gathering belt in a forage harvester row crop gathering unit.
The use of endless crop gathering belts having internal drive lugs in a forage harvester gathering unit is well known. Examples of this can be found in U.S. Pat. Nos. 3,853,016, 3,854,272, 3,888,132, and 3,940,913. Cage-like, tang, or flanged sprockets are utilized in these references.
A problem which occurs with the use of these belts and sprockets in crop gathering is that crop debris in the form of small pieces of crop can accumulate behind the belts on or in the sprockets. Debris in longer pieces can become wrapped around the sprocket or its mounting spindle. In either case, a sufficient accumulation of debris can throw the belts off the sprocket, especially driving sprockets, or at least lift the belt far enough from its driving sprocket to cause the sprocket to slip beneath the belt, defeating its purpose. Such a debris accumulation could also stretch the belt thus shortening its life or, indeed, break it. Wrapping of crops on the sprocket or spindle tends to feed upon itself and adversely affect bearing life. In extreme cases, the flow of crop through the gathering passages could be obstructed.
In U.S. Pat. No. 3,472,563 a self-cleaning belt and sprocket are taught for use on snowmobiles. The sprocket is similar in some respects to that taught herein. A major exception is that the belt lug pockets formed by the sprocket teeth have no bottoms which extend to the center hub producing a cage-like structure. Our experience in removing crop debris, especially moist and sticky debris or mud, from belt sprockets indicates that the debris must be forced out of the pocket. Without a complete pocket, including a bottom which closely fits the belt lug, this type of crop debris is not easily expelled. In U.S. Pat. No. 3,948,110 complete pockets are provided. However, the inner portion of the pocket and bottom portion meet at nearly right angles creating a corner. Drier debris can become lodged or wedged in this area and moist material would stick in the corner and build an accumulation.
Another aspect of cleaning sprockets is providing a side to side cleaning action by having the pitch of the tangs exceed slightly the pitch of the belt as will be explained below. Sprockets of the type shown in U.S. Pat. No. 3,853,016 have been so designed. However, if the pocket bottom does not closely fit the belt lug, debris cleaning action can be lost.